Dehumidifiers heat to a surface temperature of around 100-120 degrees Fahrenheit. The heat creates a natural convection that slowly circulates warm, dry air throughout an enclosure on a 24 hour basis. This increases the temperature of the air inside to several degrees above the ambient outside temperature. Expansion of the heated air forces the moist air outside through the small cracks on gun safe doors leaving the dry air inside. It is best utilized when mounting horizontally at the bottom of the safe to work effectively. It can be mounted against a wall as well. Lowering the humidity is a slow process. If you do not see the reduction of humidity after a couple of weeks then you may want to consider a larger unit.